The objective of this proposal is to determine in the perinatal lung the regulation of metabolism of PAF and to determine the regulation and distribution of PAF receptors. The two specific aim are to 1) determine the regulation of PAF metabolism via its synthesis by acetyltransferase and CDPcholine:CPTrase enzymes and via its catabolism by acetylhydrolase enzyme; and 2) characterize the distribution of PAF receptors and binding of PAF to its receptors in the lung as a function of age. Experiments will be done in lung parenchymal tissue, isolated intrapulmonary arteries and veins, and in endothelial cell cultures from pulmonary arteries and veins of full term fetuses, less than 1 day old lambs, and 6-12 day old lambs.